The present invention relates to a hydraulic circuit construction for a power shift transmission, and more particularly to a hydraulic circuit construction for a power shift transmission wherein a hydraulically operable clutch is disengaged in response to a neutral position assumed by a change speed device and is engaged in response to change speed positions assumed by the change speed device.
A known power shift transmission of this type comprises a hydraulically operable multidisk type clutch connected in series to a propelling drive transmission line, and a valve linked to a change speed device of the propelling drive transmission line for engaging and disengaging the clutch in response to operations of the change speed device.
Where only the valve is provided for operating the hydraulic clutch, the pressure of oil supplied to the clutch increases within a very short time when the clutch is engaged. This results in a shock occurring as the clutch is engaged.
In order to solve this problem it is conceivable to provide a throttle valve on an oil passage for supplying the oil to cause the pressure of oil supplied to the clutch to increase gently. However, this solution gives rise to a different problem of slackening an entire operating stroke for disengaging the clutch. It has a further disadvantage that, since the throttle valve is operative also when the clutch is engaged, the clutch tends to slip in the event of leakage at the engaged clutch.